Multiple Choice
Which of the following substances has a standard enthalpy of formation equal to zero at 25°C and 1 atm?
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8. Thermochemistry
Enthalpy of Formation
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In the context of enthalpy of formation, what does it mean when the enthalpy change (ΔH) for a reaction is negative?
A
The reaction releases energy to the surroundings and is exothermic.
B
The reaction occurs only at high temperatures.
C
The reaction does not involve any energy change.
D
The reaction absorbs energy from the surroundings and is endothermic.
Verified step by step guidance1
Understand that the enthalpy change (\$\Delta H\$) for a reaction represents the heat absorbed or released during the reaction at constant pressure.
Recognize that a negative value of \$\Delta H\$ means the system is losing heat to the surroundings.
Recall that when heat is released to the surroundings, the reaction is called exothermic.
Contrast this with a positive \$\Delta H\$, which indicates heat absorption and an endothermic reaction.
Therefore, a negative \$\Delta H\$ means the reaction releases energy to the surroundings and is exothermic.
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